Screening for explosive materials and illegal narcotics is now routine in airports, train stations, sports arenas, and other industries charged with handling large volumes of individuals, individuals and their belongings must be screened for explosive materials and explosive residues. While it is desirable to identify individuals carrying illegal narcotics, it is particularly important from a security standpoint, to screen individuals for the presence of explosive materials. Trace amounts of explosive materials remain on the skin of an individual who has handled them, because trace explosive materials are difficult to remove. Thus, trace amounts of explosive materials are transferred to articles and documents handled by an individual with explosive-contaminated hands. For example, investigation of particle transfer mechanisms from contaminated hands to documents using the explosive materials Semtex, TNT and nitroglycerin show that traces of these compounds can be detected on hands up to 48 hours after handling the materials. Consequently, screening and individual's articles and documents for trace amounts of explosive materials provides a reliable means for detecting explosive materials present on an individual or in their belongings. Because not every individual will have luggage or other article with them, screening an article, such as a travel ticket, boarding pass, passport or other identification card, or credit card is a non-invasive means of testing the individual's hands for the presence of explosive materials illegal narcotics.
Several methods have been used to for the screening of documents. One method involves manually rubbing each individual article with a swab (referred to as the “dry transfer technique”), placing the swab into an ion mobility spectrometer (IMS) sample holder, heating the sample to thermally desorb the sample, and analyzing the sample by IMS. Although it has been established that this method is optimal for trace detection of explosive materials present on an article or article, this method is cumbersome, time-consuming, and potentially inconsistent because each article must be handled individually the sample collection step is subject to human error, such as failure to apply sufficient pressure when obtaining a sample.
Another technique employs infrared heating of an article to vaporize a sample to be analyzed. This method suffers significant drawbacks. First, the indiscriminate nature of the infrared vaporization releases a complex mixture of compounds from an article, including natural oils on fingers, ink components, binders and fillers used in the manufacture of the ticket or article stock. Because the vaporization can yield a very complex sample, detection and analysis of the sample require a tandem mass spectrometer (MS-MS) to qualify the species present. Second, the paper stock used for tickets and other documents can be heat-sensitive, making the end product very susceptible to physical and chemical degradation as a result of direct heating.
For example, a direct heating method, using infrared to heat an article, e.g. a boarding pass, was developed by MSA/Sciex. A stream of air flowed through the article and passed into the ionization region of an MS-MS carries vaporized components from the pass to the ionization region. In order to vaporize non-volatile explosive materials, such as RDX, TNT and PETN, the temperature of the heating source is increased to 150-180° C. At these temperatures damage to the article can occur, including damage to a ticket having a magnetic strip.
Thus, there is a need in the art for a simple, rapid means for screening documents for trace analytes.